Steam generator and method of securing tubes within a steam generator against vibration

ABSTRACT

A steam generator includes a tube bundle having a plurality of tubes, arranged in rows and columns. The first column of tubes includes a first tube having a curved center line disposed in a first plane. The second column of tubes includes a second tube having a curved center line disposed in a second plane, the second plane being parallel to and spaced a distance from the first plane. The steam generator further includes a first number of solid anti-vibration bars disposed between the first column of tubes and the second column of tubes; wherein each of the tubes has a tube outer diameter; and wherein each of the first number of anti-vibration bars has a thickness generally transverse to the first and second planes, the thickness being greater than the distance between the first and second planes minus the tube outer diameter.

BACKGROUND

1. Field

The disclosed concept pertains generally to a steam generator, and in particular to a steam generator including anti-vibration bars. The disclosed concept also pertains to a method of securing tubes in a steam generator against vibration with a number of anti-vibration bars.

2. Background Information

Heat exchangers having tube bundles are commonly employed in pressurized water nuclear reactor systems. A steam generator generally comprises a vertically oriented shell, a tube bundle formed of tubes which each comprise two vertical components that meet at a bend portion, a tube sheet for supporting the tubes at the ends opposite the bend portion, a dividing plate that cooperates with the tube sheet and a hemispheric channel head to form a primary fluid inlet header at one end of the tube bundle and a primary fluid outlet header at the other end of the tube bundle. A primary fluid inlet nozzle is in fluid communication with the primary fluid inlet header and a primary fluid outlet nozzle is in fluid communication with the primary fluid outlet header. The steam generator secondary side comprises a wrapper disposed between the tube bundle and the shell to form an annular chamber made up of the shell on the outside and the wrapper on the inside, and a feedwater ring disposed above the bend portion of the tube bundle.

The primary fluid having been heated by circulation through the reactor core enters the steam generator through the primary fluid inlet nozzle. From the primary fluid inlet nozzle, the primary fluid is conducted through the primary fluid inlet header, through the inside of the tube bundle, out the primary fluid outlet header, through the primary fluid outlet nozzle to the reactor coolant pump for recirculation. At the same time, feedwater is introduced to the steam generator secondary side through a feedwater nozzle which is connected to the feedwater ring inside the steam generator. Upon entering the steam generator, the feedwater mixes with water returning from moisture separators positioned above the tube bundle referred to as the recirculation stream. This mixture, called the downcomer flow, is conducted down the annular chamber between the shell and the wrapper until the tube sheet near the bottom of the annular chamber causes the water to change direction, passing in heat exchange relationship with the outside of the tubes and up through the inside of the wrapper. While the water is circulating in heat exchange relationship with the tube bundle, heat is transferred from the primary fluid in the tubes to the water surrounding the tubes, causing a portion of the water outside the tubes to be converted to steam. The steam-water mixture then rises and is conducted through a number of moisture separators that separate any entrained water from the steam, and the steam vapor then exits the steam generator and is circulated typically through a turbine generator to generate electricity in a manner well known in the art.

The portion of the steam generator primarily including the bend portion of the tubes and below to the channel head is typically referred to as the evaporator section. The portion of the steam generator above the tubes that includes the moisture separators is typically referred to as the steam drum. Feedwater enters the steam generator through an inlet nozzle which is disposed in the upper portion of the cylindrical shell. The feedwater is distributed and mixed with water removed by the moisture separators and then flows down the annular channel surrounding the tube bundle.

The tubes are supported at their open ends by conventional means whereby the ends of the tubes are welded to the tube sheet which is disposed generally transverse to the longitudinal axis of the steam generator. A series of tube support plates or grids arranged in an axial spaced relationship to each other are provided along the straight portion of the tubes in order to support the straight section of the tubing. Regarding the tube bundle, various steam generators utilize different tube configurations, for example wherein the bend portion is curved or U-shaped, or wherein the vertical components of the tubes each bend at sharp angles, forming a relatively horizontal shaped bend portion.

Located within the bend portion of the tubes are a plurality of anti-vibration bars which are typically disposed between each column of tubes. The anti-vibration bars provide support and do not substantially interfere with the flow of the moisture laden steam. The anti-vibration bars are intended to prevent excessive vibrations of the individual tubes of the entire tube bundle; vibrations which can potentially damage the tubes. It is well known that the bend portion of the tube bundle is more severely affected by the vibrations, and, because of the bend configuration, more difficult to adequately support in order to eliminate the vibrations.

Typical motion of the tubes experiencing normal vibration is transverse to the plane of the U-bend and therefore such vibration is referred to as out-of-plane vibration. Under unusual conditions, tubes can also experience in-plane vibration. In such situations, adjacent tubes in a given column can contact one another, resulting in severe damage to the tubes. The manufacturing and assembly of the tube bundle are major obstacles to a mechanical solution to this problem. Hence, current anti-vibration bar assembly designs do not significantly restrict in-plane motion of the tubes.

SUMMARY

These needs and others are met by the disclosed concept in which a solid anti-vibration bar having an increased thickness is structured to be located within a tube bundle.

In accordance with one aspect of the disclosed concept, a steam generator is provided. The steam generator has a primary side for circulating a heated fluid and a secondary side for circulating a fluid to be heated by the heated fluid circulating in the primary side. The steam generator includes: a channel head for receiving the heated fluid; a tube sheet that separates the channel head from the secondary side; a tube bundle having a plurality of tubes, arranged in rows and columns, the tube bundle extending from the channel head, through the tube sheet and through at least a portion of the secondary side; and a first number of solid anti-vibration bars. The plurality of tubes includes a first column of tubes, the first column of tubes comprising a first tube having a curved center line disposed in a first plane. The plurality of tubes further includes a second column of tubes, each of the first number of anti-vibration bars being disposed between the first column of tubes and the second column of tubes. The second column of tubes comprises a second tube having a curved center line disposed in a second plane, the second plane being parallel to and spaced a distance from the first plane. Each of the tubes has a tube outer diameter. Each of the first number of anti-vibration bars has a thickness generally transverse to the first and second planes. The thickness of each of the first number of anti-vibration bars is greater than the distance between the first and second planes minus the tube outer diameter.

In accordance with another aspect of the disclosed concept, a method is provided for securing tubes within a steam generator against vibration, the tubes being disposed in a tube bundle and arranged in rows and columns, with lanes between the columns. The method comprises: providing a first column of tubes, the first column of tubes comprising a first tube having a curved center line disposed in a first plane; providing a first number of solid anti-vibration bars; and providing a second column of tubes, each of the first number of anti-vibration bars being disposed between the first column of tubes and the second column of tubes, the second column of tubes comprising a second tube having a curved center line disposed in a second plane, the second plane being parallel to and spaced a distance from the first plane. Each of the tubes has a tube outer diameter. Each of the first number of anti-vibration bars has a thickness generally transverse to the first and second planes. The thickness of each of the first number of anti-vibration bars is greater than the distance between the first and second planes minus the tube outer diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view, partially cut away, of a vertical tube and shell steam generator;

FIG. 2 is a schematic, cross-section of a portion of a tube bundle of a steam generator with anti-vibration bars;

FIG. 3 is a schematic, cross-section of a portion of a tube bundle of a steam generator with anti-vibration bars in accordance with an embodiment of the disclosed concept;

FIG. 4A is schematic front view of a number of tubes of the tube bundle of FIG. 3;

FIG. 4B is a schematic side view of the tubes of FIG. 4A;

FIG. 4C is a schematic isometric view of the tubes of FIG. 4A;

FIG. 5 is a schematic, cross-section of a portion of a tube bundle of a steam generator with anti-vibration bars in accordance with an alternative embodiment of the disclosed concept;

FIG. 6A is a schematic, cross-section of a portion of a tube bundle of a steam generator with anti-vibration bars in accordance with a further embodiment of the disclosed concept;

FIG. 6B is a schematic, cross-section of the tube bundle of FIG. 6A with the anti-vibration bars being displaced; and

FIG. 7 is a schematic, cross-section, of a portion of a tube bundle of a steam generator with anti-vibration bars in accordance with an additional embodiment of the disclosed concept.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIG. 1 shows a steam generator 2 that utilizes a plurality of heat exchanger tubes 3 which form a tube bundle 4 to provide the heating surface required to transfer heat from the primary fluid to vaporize or boil the secondary fluid. The steam generator 2 comprises a vessel having a vertically oriented tubular shell portion 6 and a top enclosure or dished head 8 enclosing the upper end and a generally hemispherical-shaped channel head 10 enclosing the lower end. The lower shell portion 6 is smaller in diameter than the upper shell portion 12 and a frustoconical-shaped transition 14 connects the upper portion and lower portions. A tube sheet 16 is attached to the channel head 10 and has a plurality of holes 18 disposed therein to receive ends of the tubes 3. A dividing plate 22 is centrally disposed within the channel head 10 to divide the channel head 10 into two compartments 24,26, which serve as headers for the tube bundle 4. Compartment 26 is the primary fluid inlet compartment and has a primary fluid inlet nozzle 27 in fluid communication therewith. Compartment 24 is the primary fluid outlet compartment and has a primary fluid outlet nozzle 28 in fluid communication therewith. Thus, primary fluid, i.e., the reactor coolant, which enters fluid compartment 26 is caused to flow through the tube bundle 4 and out through outlet nozzle 28.

The tube bundle 4 is encircled by a wrapper 30 which forms an annular passage 32 between the wrapper 30 and the shell and transition portions 6,14, respectively. The top of the wrapper 30 is covered by a lower deck plate 34 which includes a plurality of openings 36 in fluid communication with a plurality of riser tubes 38. Swirl vanes 40 are disposed within the riser tubes 38 to cause steam flowing therethrough to spin and centrifugally remove some of the moisture contained within the steam as it flows through this primary centrifugal separator. The water separated from the steam in this primary separator is returned to the top surface of the lower deck plate 34. After flowing through the primary centrifugal separator, the steam passes through a secondary separator 42 before reaching a steam outlet nozzle 44 centrally disposed in the dished head 8. The water separated from the steam in the secondary separator 42 is returned to mix with the water returned from the primary separator above the lower deck plate 34.

The feedwater inlet structure of this steam generator 2 includes a feedwater inlet nozzle 46 having a generally horizontal portion called a feedring 48 and discharge nozzles 50 elevated above the feedring 48. Feedwater, which is supplied through the feedwater inlet nozzle 46, passes through the feedwater ring 48, exits through the discharge nozzles 50 and mixes with water which was separated from the steam and is recirculated. The mixture then flows down above the lower deck plate 34 into the annular downcomer passage 32. The water then enters the tube bundle 4 at the lower portion of the wrapper 30 and flows among the tubes 3 and up the tube bundle 4 where it is heated to generate steam.

As previously mentioned, the tube bundle 4 has a plurality of anti-vibration bars (not shown in FIG. 1) located between the tubes 3. FIG. 2 shows a portion of a tube bundle 100 that includes a number of columns of tubes 110,130,150. Located between the first column of tubes 110 and the second column of tubes 130 is an anti-vibration bar 120. Located between the second column of tubes 130 and the third column of tubes 150 is an anti-vibration bar 140. The anti-vibration bar 120 has a thickness 122 and the anti-vibration bar 140 has a thickness 142. As seen, because the anti-vibration bars 120,140 are linear, the thicknesses 122,142 are restricted by a distance 101 between the columns of tubes 110,130,150. As a result, in operation the anti-vibration bars 120,140 do not significantly reduce the amount of possible in-plane motion within the columns of tubes 110,130,150.

As will be discussed in connection with FIGS. 3 through 7, in-plane vibration can be significantly reduced by including a number of improved anti-vibration bars 220,240,320, 460,480,520. Referring to FIG. 3, the cross section of a portion within a U-shaped bend of a tube bundle 200 of a steam generator (not shown) is shown. The tube bundle 200 includes a number of columns of tubes 210,230,250, wherein any two adjacent tubes have an equal distance 203 (subject to manufacturing tolerance) between their centers (e.g., a triangular pitch). Although the disclosed concept will be described in association with a triangular pitch, it will be appreciated that the disclosed concept could be employed with alternative orientations (e.g., without limitation, a tube bundle (not shown) with tubes having square pitch rotated 45 degrees).

The first column of tubes 210 may be either in the middle of the tube bundle 200 or may be at an end. Located between the first column of tubes 210 and the second column of tubes 230 is an anti-vibration bar 220. The anti-vibration bar 220 is solid and has a thickness 222. Referring to FIGS. 3 through 4C, the first column of tubes 210 includes a tube 212 that has a curved center line 214 located in a plane 216. Similarly, the second column of tubes 230 includes a tube 232 that has a curved center line 234 located in a plane 236. As seen in FIG. 3, the plane 216 and the plane 236 are parallel and are spaced apart by a distance 206. The distance 206 is substantially equal to two times an outer radius 202 (e.g., a tube outer diameter 204) plus a distance 201. The distance 201 corresponds to the distance 101 shown in FIG. 2.

As seen in FIG. 3, the thickness 222 of the anti-vibration bar 220 is generally transverse to the planes 216,236 and is greater than the distance 201 between the columns of tubes 210,230. Continuing to refer to FIG. 3, located between the second column of tubes 230 and the third column of tubes 250 is a second anti-vibration bar 240. Similar to the anti-vibration bar 220, the anti-vibration bar 240 is solid and has a thickness 242. Referring to FIGS. 3 through 4C, the third column of tubes 250 includes a tube 252 that has a curved center line 254 located in a plane 256. The plane 256 is parallel to and spaced a distance 208 from the plane 236. The distance 208 is substantially equal to two times the radius 202 (e.g., the tube outer diameter 204) plus the distance 201.

Similar to the thickness 222 of the anti-vibration bar 220, the thickness 242 of the anti-vibration bar 240 is generally transverse to planes 236,256 and is greater than the distance 201 between the columns of tubes 230,250. In operation, this increased thickness prevents significant in-plane (see, for example, planes 216,236,256) motion in the columns of tubes 210,230,250, advantageously corresponding to a significant decrease in in-plane vibration within the tube bundle 200. As seen in FIG. 3, the anti-vibration bar 220 includes a number of bends 224 that are curved and are structured to wind between the first column of tubes 210 and the second column of tubes 230.

Similarly, the anti-vibration bar 240 includes a number of bends 244 that are curved and are structured to wind between the second column of tubes 230 and the third column of tubes 250. The bends 224,244 enable the thicknesses 222,242 of the anti-vibration bars 220,240 to be greater than the thicknesses 122,142 of the anti-vibration bars 120,140. Furthermore, while the thicknesses 122,142 of the anti-vibration bars 120,140 are no greater than the distance 101, the thicknesses 222,242 of the anti-vibration bars 220,240 are only limited by the distance 203 between adjacent centers minus two times the radius 202 (e.g., the tube outer diameter 204).

FIG. 5 shows a portion within a U-shaped bend of a tube bundle 300 of a steam generator (not shown) in accordance with an alternative embodiment of the disclosed concept. As seen, the tube bundle 300 includes an anti-vibration bar 320 that is located between a first column of tubes 310 and a second column of tubes 330. The first column of tubes 310 may be either in the middle of the tube bundle 300 or may be at an end. Furthermore, the first column of tubes 310 includes a tube 312 that has a curved center line (not shown) that is located in a plane 316. The second column of tubes 330 includes a tube 332 that has a curved center line (not shown) that is located in a plane 336. The plane 336 is parallel to and spaced a distance 306 from the plane 316. Similar to the anti-vibration bars 220,240, the anti-vibration bar 320 has a thickness 322. The thickness 322 is generally transverse to the planes 316,336 and is greater than a distance 301 between the columns of tube 310,330.

As seen, the distance 301 corresponds to the distance 306 minus two times a radius 302 (e.g., a tube outer diameter 304). In a similar manner as the anti-vibration bars 220,240, the anti-vibration bar 320 is structured to wind between the first column of tubes 310 and the second column of tubes 330. However, while the anti-vibration bars 220,240 include a number of bends 224,244 that are curved, the anti-vibration bar 320 includes a number of bends 324 that are substantially jagged. The bends 324 of the anti-vibration bar 320, like the bends 224,244 of the anti-vibration bars 220,240, allow the anti-vibration bar 320 to have the increased thickness 322. Furthermore, similar to the anti-vibration bars 220,240, in operation, the increased thickness 322 of the anti-vibration bar 320 prevents significant in-plane (see, for example, planes 316,336) motion with the columns of tubes 310,330 advantageously corresponding to a significant decrease in in-plane vibration within the tube bundle 300.

FIG. 6A shows a portion within a U-shaped bend of a tube bundle 400 which includes a number of anti-vibration bars 460,480. The anti-vibration bar 460 is located between a first column of tubes 410 and a second column of tubes 430. The first column of tubes 410 may be either in the middle of the tube bundle 400 or may be at an end. The anti-vibration bar 480 is located between the second column of tubes 430 and a third column of tubes 450. Similar to the anti-vibration bars 220,240, the anti-vibration bars 460,480 include a number of bends 464,484 that are structured to wind between the columns of tubes 410,430,450. However, the anti-vibration bars 460,480 are less thick than the anti-vibration bars 220,240.

As seen in FIG. 6A, the first column of tubes 410 includes a tube 412 and the second column of tubes 430 includes a tube 432, the anti-vibration bar 460 being situated adjacent the tubes 412,432. Since the anti-vibration bar 460 is less thick, there are gaps (see, for example, gap 467) between the anti-vibration bar 460 and the tubes 412,432. Similarly, the anti-vibration bar 480 is situated adjacent the tube 432 and each of the tubes in the third column of tubes 450. Since the anti-vibration bar 480 is less thick, there are gaps (see, for example, gap 487) between the anti-vibration bar 480 and the tubes in the second column of tubes 430 and the third column of tubes 450.

As seen, the anti-vibration bar 460 is substantially located along a longitudinal axis 465 and the anti-vibration bar 480 is substantially located along a longitudinal axis 485. FIG. 6B shows a portion of a tube bundle 400′ in which the anti-vibration bars 460,480 have been displaced along the longitudinal axes 465,485. As seen in FIGS. 6A and 6B, the anti-vibration bar 460 is displaced in a first direction 461 along the longitudinal axis 465. The anti-vibration bar 480 is displaced in a second direction 481 along the longitudinal axis 485. The first direction 461 and the second direction 481 are substantially parallel to and opposite each other. The anti-vibration bars 460,480 may be displaced by being pulled and/or pushed after fabrication of the tube bundle by an operator or by the use of a suitable mechanism known in the art.

As seen in FIG. 6B, as the anti-vibration bar 460 moves in the first direction 461 along the longitudinal axis 465, the anti-vibration bar 460 engages the tube 412 such that there is no gap (or the gap 467 seen in FIG. 6A substantially decreases in size). Similarly, as the anti-vibration bar 480 moves in the second direction 481 along the longitudinal axis 485, the anti-vibration bar 480 engages the tube 432 such that there is no gap (or the gap 487 seen in FIG. 6A substantially decreases in size). In this manner, gaps (see, for example, gaps 467,487 in FIG. 6A) between the anti-vibration bars 460,480 and tubes in the columns of tubes 410,430,450 decrease in size, further reducing the amount of possible in-plane motion.

FIG. 7 shows a portion within a U-shaped bend of a tube bundle 500 of a steam generator (not shown) in accordance with an alternative embodiment of the disclosed concept. As seen, the tube bundle 500 includes a number of columns of tubes 510,530,550. The first column of tubes 510 may be either in the middle of the tube bundle 500 or may be at an end. Located between the first column of tubes 510 and the second column of tubes 530 is an anti-vibration bar 520. The anti-vibration bar 520 is substantially similar to the anti-vibration bars 220,240, having a thickness 522 generally transverse to planes 516,536 and greater than a distance 501 between the columns of tubes 510,530.

Located between the second column of tubes 530 and the third column of tubes 550 is an anti-vibration bar 540 that is substantially similar to the anti-vibration bars 120,140 seen in FIG. 2. The anti-vibration bar 540 has a thickness 542 that is generally transverse to the plane 536, which is parallel to and spaced a distance 508 from a plane 556. The thickness 542 of the anti-vibration bar 540 is less than the thickness 522 of the anti-vibration bar 520. Similar to the thicknesses 122,142 of the anti-vibration bars 120,140, the thickness 542 is restricted by the distance 501 and may be substantially equal to, but no more than the distance 501. As seen, the anti-vibration bar 540 is substantially linear, having no bend or curvature along its longitudinal axis.

In this manner, in-plane vibration within the tube bundle 500 can be significantly reduced by including the anti-vibration bar 520, while costs can advantageously be saved by including the anti-vibration bar 540 in accordance with existing designs. FIG. 7 shows one of many alternative embodiments that are within the scope of the disclosed concept. For example and without limitation, it is within the scope of the disclosed concept to have any number of the anti-vibration bars 220,240,320,460,480,520 that are arranged in any configuration with existing anti-vibration bars 120,140,540. Additionally, it is further understood that the anti-vibration bars 220,240,320,460,480,520,540 are secured to a structure or structures (not shown) extending around the tube bundle bends in one of several manners known in the art.

The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.

As employed herein, the term “solid” shall mean being without an internal cavity or opening. As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality). 

What is claimed is:
 1. A steam generator having a primary side for circulating a heated fluid and a secondary side for circulating a fluid to be heated by the heated fluid circulating in the primary side, the steam generator comprising: a channel head for receiving the heated fluid; a tube sheet that separates the channel head from the secondary side; a tube bundle having a plurality of tubes, arranged in rows and columns, the tube bundle extending from the channel head, through the tube sheet and through at least a portion of the secondary side; and a first number of solid anti-vibration bars; wherein the plurality of tubes comprises: a first column of tubes, the first column of tubes comprising a first tube having a curved center line disposed in a first plane, and a second column of tubes, each of the first number of anti-vibration bars being disposed between the first column of tubes and the second column of tubes, the second column of tubes comprising a second tube having a curved center line disposed in a second plane, the second plane being parallel to and spaced a distance from the first plane, wherein each of the tubes has a tube outer diameter; wherein each of the first number of anti-vibration bars has a thickness generally transverse to the first and second planes; and wherein the thickness of each of the first number of anti-vibration bars is greater than the distance between the first and second planes minus the tube outer diameter.
 2. The steam generator of claim 1 wherein each of the first number of anti-vibration bars comprises a number of bends; wherein the bends of each of the first number of anti-vibration bars wind between the first column of tubes and the second column of tubes; and wherein the bends of each of the first number of anti-vibration bars are curved.
 3. The steam generator of claim 1 wherein each of the first number of anti-vibration bars comprises a number of bends; wherein the bends of each of the first number of anti-vibration bars wind between the first column of tubes and the second column of tubes; and wherein the bends of each of the first number of anti-vibration bars are substantially jagged.
 4. The steam generator of claim 1 further comprising a second number of solid anti-vibration bars; wherein the plurality of tubes further comprises a third column of tubes; wherein each of the second number of anti-vibration bars is disposed between the second column of tubes and the third column of tubes; wherein the third column of tubes comprises a third tube having a curved center line disposed in a third plane; wherein the third plane is parallel to and spaced a distance from the second plane; wherein each of the second number of anti-vibration bars has a thickness generally transverse to the second and third planes; and wherein the thickness of each of the second number of anti-vibration bars is greater than the distance between the second and third planes minus the tube outer diameter.
 5. The steam generator of claim 4 wherein the plurality of tubes have a triangular pitch; wherein the tube bundle comprises a U-shaped bend; and wherein each of the first number of anti-vibration bars and the second number of anti-vibration bars is disposed in the U-shaped bend.
 6. The steam generator of claim 4 wherein the plurality of tubes have a rotated square pitch; wherein the tube bundle comprises a U-shaped bend; and wherein each of the first number of anti-vibration bars and the second number of anti-vibration bars is disposed in the U-shaped bend.
 7. The steam generator of claim 4 wherein each of the first number of anti-vibration bars and the second number of anti-vibration bars comprises a number of bends; wherein the bends of each of the first number of anti-vibration bars wind between the first column of tubes and the second column of tubes; and wherein the bends of each of the second number of anti-vibration bars wind between the second column of tubes and the third column of tubes.
 8. The steam generator of claim 1 further comprising a second number of anti-vibration bars; wherein the plurality of tubes further comprises a third column of tubes; wherein each of the second number of anti-vibration bars is disposed between the second column of tubes and the third column of tubes; wherein the third column of tubes comprises a third tube having a curved center line disposed in a third plane; wherein the third plane is parallel to and spaced a distance from the second plane; wherein each of the second number of anti-vibration bars has a thickness generally transverse to the second and third planes; and wherein the thickness of each of the second number of anti-vibration bars is less than the thickness of each of the first number of anti-vibration bars.
 9. The steam generator of claim 8 wherein the thickness of each of the second number of anti-vibration bars is substantially equal to the distance between the second and third planes minus the tube outer diameter.
 10. A method of securing tubes within a steam generator against vibration, the tubes being disposed in a tube bundle and arranged in rows and columns, with lanes between the columns, the method comprising: providing a first column of tubes, the first column of tubes comprising a first tube having a curved center line disposed in a first plane; providing a first number of solid anti-vibration bars; and providing a second column of tubes, each of the first number of anti-vibration bars being disposed between the first column of tubes and the second column of tubes, the second column of tubes comprising a second tube having a curved center line disposed in a second plane, the second plane being parallel to and spaced a distance from the first plane; wherein each of the tubes has a tube outer diameter; wherein each of the first number of anti-vibration bars has a thickness generally transverse to the first and second planes; and wherein the thickness of each of the first number of anti-vibration bars is greater than the distance between the first and second planes minus the tube outer diameter.
 11. The method of claim 10 wherein each of the first number of anti-vibration bars comprises a number of bends; wherein the bends of each of the first number of anti-vibration bars wind between the first column of tubes and the second column of tubes; and wherein the bends of each of the first number of anti-vibration bars are curved.
 12. The method of claim 10 wherein each of the first number of anti-vibration bars comprises a number of bends; wherein the bends of each of the first number of anti-vibration bars wind between the first column of tubes and the second column of tubes; and wherein the bends of each of the first number of anti-vibration bars are substantially jagged.
 13. The method of claim 10 further comprising: providing a second number of solid anti-vibration bars; and providing a third column of tubes, each of the second number of anti-vibration bars being disposed between the second column of tubes and the third column of tubes, the third column of tubes comprising a third tube having a curved center line disposed in a third plane, the third plane being parallel to and spaced a distance from the second plane; wherein each of the second number of anti-vibration bars has a thickness generally transverse to the second and third planes; and wherein the thickness of each of the second number of anti-vibration bars is greater than the distance between the second plane and third planes minus the tube outer diameter.
 14. The method of claim 13 wherein the first number of anti-vibration bars comprises a first anti-vibration bar substantially disposed along a first longitudinal axis; wherein the second number of anti-vibration bars comprises a second anti-vibration bar substantially disposed along a second longitudinal axis parallel to the first longitudinal axis; wherein the first anti-vibration bar is disposed adjacent the first tube and the second tube; wherein the second anti-vibration bar is disposed adjacent the second tube and the third tube; wherein there is a first gap between the first anti-vibration bar and the first tube and a second gap between the first anti-vibration bar and the second tube; and wherein there is a third gap between the second anti-vibration bar and the second tube and a fourth gap between the second anti-vibration bar and the third tube, the method further comprising: displacing the first anti-vibration bar in a first direction along the first longitudinal axis; and displacing the second anti-vibration bar in a second direction along the second longitudinal axis, the second direction being opposite the first direction, each of the first gap, the second gap, the third gap, and the fourth gap having a size that decreases as the first anti-vibration bar is displaced in the first direction and the second anti-vibration bar is displaced in the second direction.
 15. The method of claim 14 wherein the tubes have a triangular pitch; wherein the tube bundle comprises a U-shaped bend; and wherein each of the first number of anti-vibration bars and the second number of anti-vibration bars is disposed in the U-shaped bend.
 16. The method of claim 14 wherein the tubes have a rotated square pitch; wherein the tube bundle comprises a U-shaped bend; and wherein each of the first number of anti-vibration bars and the second number of anti-vibration bars is disposed in the U-shaped bend.
 17. The method of claim 14 wherein each of the first number of anti-vibration bars and the second number of anti-vibration bars comprises a number of bends; wherein the bends of each of the first number of anti-vibration bars wind between the first column of tubes and the second column of tubes; and wherein the bends of each of the second number of anti-vibration bars wind between the second column of tubes and the third column of tubes.
 18. The method of claim 10 further comprising: providing a second number of anti-vibration bars; and providing a third column of tubes, each of the second number of anti-vibration bars being disposed between the second column of tubes and the third column of tubes, the third column of tubes comprising a third tube having a curved center line disposed in a third plane, the third plane being parallel to and spaced a distance from the second plane; wherein each of the second number of anti-vibration bars has a thickness generally transverse to the second and third planes; and wherein the thickness of each of the second number of anti-vibration bars is less than the thickness of each of the first number of anti-vibration bars.
 19. The method of claim 18 wherein the thickness of each of the second number of anti-vibration bars is substantially equal to the distance between the second and third planes minus the tube outer diameter.
 20. The method of claim 19 wherein each of the second number of anti-vibration bars has no bend or curvature along a longitudinal axis. 